Flickerless operation of electric lighting elements



Nov. 8, 1949 1.. F. BIRD 2,487,092

FLICKERLESS OPERATION OF ELECTRIC LIGHTING ELEMENTS Filed July 25, 194'?I N V EN TOR. [es/er Ifizkd ATTORNEY Patented Nov. 8, 1949 UNITED STATESPATENT OFFICE FLICKERLESS OPERATION OF ELECTRIC LIGHTING ELEMENTS '7Claims. 1

This invention relates to an improvement in the flickerless operation ofelectric lighting elements and employs a frequency multiplication systemin connection with the operation of such elements, such as fluorescentlamps and neon advertising signs, from standard commercial lightingfrequencies.

The principal object of my invention is to secure flicker free lightfrom electric discharge tubes and the like operating on a low frequencyalternating current supply line, in an economical and simple manner.

Another object is to provide a single system from which a number ofdischarge tubes or the like may be so operated.

A further object is to obtain the desired results without the use ofexpensive parts or parts subject to wear and disorder.

A still further object is to have a system that reduces the efiects ofsupply line voltage fluctuation and produces an output of lightsubstantially free from variations.

It is well known that electric discharge tubes of the types described donot give off light continuously at a uniform intensity but give it offin pulses at twice the frequency of the supply line voltage. Eye strainfrequently results from prolonged use of fluorescent lamps operating ona 60 cycle suppl line. When the supply line frequency is below 50 cyclesper second, the pulsations of light become apparent to the human eye inthe form of an annoying flicker, and when only a 40 cycle supply isutilized the flicker becomes so pronounced that a tube of this nature isno longer usable as a reading lamp.

I obtain flicker free light from electric discharge tubes by utilizingcertain applications of electrical circuit design by which the frequencyof the supply line is multiplied so as to be above the flicker frequencyand then use this higher frequency to operate the tubes. For example,the frequency of a cycle supply Imay multiply to 75 cycles and when adischarge tube operates on this higher frequency no flicker is apparentto the normal human eye. I do this by employing only fixed electricalcomponents such as transformers, reactors and capacitors which have nomoving parts and last indefinitely.

The following is a description of certain circuits embodying myinvention, which when read r in connection with the following drawingswill explain how I obtain the desired results.

In the drawings in which the same number represents the same or asimilar part:

Figure 1 is a frequency multiplication circuit with a certainarrangement of electrical components.

Figures 2, 3 and 4 are similar circuits, each modified to some extent bythe rearrangement, addition or omission of certain electrical comlatewithout too much reaction back on the primary circuit. It is desirablethat there be sufficient leakage reactance between the primary andsecondary windings so that the secondary kva. is limited to about 150%of the normal load power of the transformer when the secondary of thetransformer is operated under short circuit conditions.

Reactor 5 is shown in the circuit of Figure l on secondary line H as aseparate unit electrically, but actually it is built in as an integralpart of transformer l.

Across the secondary lines M and I place capacitor 8 having such areactance that at the third harmonic frequency of the supply voltage,the inductive reactance of the transformer secondary and the capacitivereactance of the condenser are equal.

Capacitor 6 and the reactance of the secondary of the transformer,therefore, form a resonant system which is resonant to the thirdharmonic frequency of the supply. In common with all resonant systems,this one will oscillate if it is excited at the proper intervals. Thesupply frequency in this case produces the necessary excitation givingthe resonant system impulses at one-third the oscillating frequency.With the proper design of transformer I and capacitor 6 considerableenergy will flow in the oscillating system and if not loaded too heavilywill deliver usable power. I find that about 6 to 12 kva.s of energymust flow in the oscillating system for each kilowatt of energydelivered to the load.

Being provided with this increased harmonic frequency the discharge tube8 can be operated in the usual manner with stabilizing ballast such asreactor 1 designed for the harmonic frequency.

While I have discussed the third harmonic frequency, it is apparent thatsome other multiple Such a circuit as I have described functions asfollows. If the inductance of the secondary coil and core structure hasa value of 126 ohms at the supply line frequency and 378 ohms at thethird harmonic frequency, the capacitor would then have a reactance of378 ohms at the harmonic frequency. Because of the loose couplingexisting between the primary and secondary coils on the core, theresonant secondary circuit is free to oscillate with but little reactionon the input circuits. That this is exactly the result is clearly shownby the manner in which this circuit reacts when connected to a variableline supply voltage. With low input very little third harmonic appearsacross the capacitor. As the input is gradually increased thefundamental and third harmonic increase together up to a certain pointwhen there is a jump in the third harmonic voltage and it becomespredominant across the capacitor. Further increase in line voltageresults in no further increase in harmonic voltage. In fact, a furtherincrease in input voltage results in a reduction in harmonic voltagealthough this effect is gradual and this system gives almost constantoutput of harmonic voltages over 15% or more of line voltage change.This effect is very desirable since it renders the harmonic voltageessentially independent of the input throughout the range of variationordinarily found in supply line voltages.

The harmonic voltages generated suffer from regulation due to loadingand this effect is not especially desired but can be eliminated by theuse of the well known regulating circuits, following the harmonicgenerating circuit so that good regulation is secured under conditionswhich avoid overloading.

In Figure 2 as well as in Figures 3 and 4 reactor 5 is not shownseparately, its function being performed by the reactance built intosecondary coil 4 of transformer I.

In Figures 3 and 4 the tube 3 is shown with auxiliary stabilizingreactance operating from only a portion of the harmonic voltagesgenerated across the capacitor. In Figure 4, single capacitor II isplaced across secondary lines l5 and I6 and reactor 1 is variablyconnected to secondary coil 4 of transformer I through line I1.

There are other modifications that may be made in the circuits describedand other circuits employed that embody my invention, and I do not limitthe scope of my invention to the specific forms herein set forth.

What I claim is:

1. An electric circuit connected to a source of alternating current,comprising a high reactance type transformer, a shunt capacitorconnected across the secondary coil of such transformer with reactanceequal to the reactance of such secondary coil at an harmonic frequencyof the supply voltage and an electric discharge tube and a reactance inseries with said tube connected to the secondary coil of suchtransformer.

2. An electric circuit connected to a source of alternating current,comprising a transformer having a primary and a secondary coil with alimited magnetic coupling between them, a shunt capacitor connectedacross such secondary coil with reactance equal to the reactance of thesecondary coil of such transformer at an harmonic frequency of thesupply voltage and an electric discharge tube and a reactance in serieswith said tube connected to the secondary coil of such transformer.

3. A substantially flicker free light producing system comprising a lowfrequency alternating current power source, a high reactance transformerincluding in addition to a primary winding a secondary winding mountedupon a magnetic core structure partially in the magnetic field generatedby the primary winding and having a substantial inductive reactance, acapacitor with reactance equal to the inductive reactance of saidsecondary coil at an harmonic frequency of the supply voltage connectedacross said secondary coil, a light producing element, and a stabilizingunit adapted to operate the light producing element at the harmonicvoltage generated in the secondary coil circuit.

4. A frequency multiplying arrangement adapted to be energized by asource of alternating current comprising, in combination, a lowfrequency alternating power source, a high reactance transformerincluding in addition to a primary winding a secondary winding mountedupon a magnetic core structure partially in the magnetic field generatedby the primary winding and having a substantial inductive reactance, acapacitor with reactance equal to the inductive reactance of saidsecondary coil at an harmonic frequency of the supply voltage connectedacross said secondary coil, a light producing element, and a stabilizingunit adapted to operate the light producing element at the harmonicvoltage generated in the secondary coil circuit.

5. In a pulsating light producing electrical system the combination of alow frequency alternating current supply with an electrical transformerhaving a magnetic core structure upon which are mounted a primarywinding and a secondary winding in spaced relation and having a highreluctance magnetic leakage path producing magnetically loose couplingbetween the primary and secondary coils, and having substantialreactance associated with the secondary winding and having connectedacross the secondary winding a capacitor resonating the secondaryreactance to an harmonic of the low frequency supply and having an arcstabilizing reactance with an electric arc lamp connected to thesecondary resonant system.

6. In a pulsating light producing electrical system the combination of alow frequency alternating current supply with an electrical transformerhaving a magnetic core structure upon which are mounted a primarywinding and a secondary winding in spaced relation and having a highreluctance magnetic leakage path producing magnetically loose couplingbetween the pri mary and secondary coils, and having substantialreactance associated with the secondary winding and having connectedacross the secondary winding a capacitor resonating the secondaryreactance to an harmonic of the low frequency supply and having an arcstabilizing reactance with an electric discharge lamp connected to thesecondary resonant system.

7. In a pulsating light producing electrical system the combination of alow frequency alternating current supply with an electrical transformerhaving a magnetic core structure upon which are mounted a primarywinding and a secondary winding in spaced relation and having a highreluctance magnetic leakage path producing magnetically loose couplingbetween the primary and secondary coils, and having substantialreactance associated with the secondary winding and having connectedacross the secondary winding a capacitor resonating the secondsREFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date Schweitzer, Jr Oct. 22, 1940McCarthy Dec. 30, 1941 Fries Dec. 15, 1942 Bridges Mar. 6, 1945

